Prior spark plugs typically provide gap electrodes that are flat and parallel or round and symmetrical (i.e., circular convex to circular concave). One such spark plug provides one or more prongs disposed over the tip of a center or sparking electrode. Such spark plugs generate a spark at the outermost tip of the center electrode which results in the gradual build-up of carbon on the tips of the central electrode and the prongs. The carbon build-up leads to a reduced capacity or failure in generating a spark for igniting the fuel/air mixture in an internal combustion engine. Further, the prongs tend to need re-gapping because of electrical use wear and any unwanted bending of the prongs which can occur during periodic cleaning of the spark plug electrodes.
In order to lengthen operational life, another type of spark plug has a disk-like terminal head concentrically located in spaced relation within a cylindrical ground electrode to provide an annular sparking gap between the ground electrode and the entire circumference of the disk-like terminal head of the sparking electrode. Thus, in this type of spark plug, firing may occur across the annular sparking gap anywhere along its circumferential length and therefore less fouling will occur as compared with spark plugs having a single point-to-point contact between a central electrode and a ground electrode prong. A drawback with spark plugs with annular sparking gaps, however, is that the center electrode and insulator are typically not exposed to enough of the fuel/air mixture to prevent fouling and are susceptible to damage resulting from, for example, accidental dropping of the spark plug. Further, the insulator member of such spark plugs typically does not have enough exposure to the fuel/air mixture for allowing sufficient cooling to prevent an associated insulator heat build-up which can in turn lead to cracking or insulator resistance breakdown.
In view of the foregoing, it is a general object of the present invention to provide a spark plug which overcomes the above-mentioned drawbacks associated with the use and operational life of prior art spark plugs.